The impetus was an argument between the deputy's son and another person, sources say.

A veteran Los Angeles County sheriff's deputy was arrested Wednesday for allegedly shooting and killing a man in Sylmar while off-duty in June, authorities said.

The deputy, Francisco Gamez, 41, has been with the department for 17 years and was last working as a station detective in West Hollywood.

Law enforcement sources told The Times that the deputy's son got into a dispute with another person. The son, they said, called his father to the scene. The deputy allegedly drove up soon after and exchanged words before opening fire from inside his car, striking one man, the sources said.

He then allegedly drove a short distance before shooting at a second person, added the sources, who asked for anonymity because the investigation is ongoing.

That person was not injured, according to authorities.

The other victim, Armando Casillas, 38, was taken to a hospital, where he was pronounced dead from a gunshot wound to the chest just before midnight on June 17.

FOR THE RECORD:An earlier version of this article misspelled the victim's first name as Armondo.

Neighbors said Gamez and Casillas lived a block apart.

In August, a person who identified himself as the victim's brother commented on the website of the Los Angeles Times, saying he suspected a deputy was responsible.

"We think he is a L.A. COUNTY SHERIFF," the comment stated. "The reason we think he is a Sheriff is that he shouted to my Brother "L.A. COUNTY SHERIFF WHERE YOU FROM" as if the sheriff was in a gang."

The person who wrote the comment could not be reached Wednesday evening.

At the time of the killing, authorities said the victim got into an argument with an unknown person. At some point, the other person left the area only to return and shoot Casillas in a drive-by, authorities said then. Now they are saying that the shooter was not the same person who initially got into the argument.

LAPD officers arrested Gamez on suspicion of murder, attempted murder and use of a firearm in the commission of a felony. He was booked into the LAPD's 77th Street station Wednesday in lieu of $4-million bail, officials said. He has not been charged.

Casillas' sister said that the family was thankful for the arrest, but that they were not prepared to discuss the events that led to the fatal shooting.

In a statement, Sheriff Lee Baca called the incident "deeply disturbing."

His spokesman Steve Whitmore said the department placed Gamez on leave July 3 after learning from the LAPD about the investigation.

"He's been stripped of all law enforcement power," Whitmore said. "It casts a pall over the scores and scores of deputy sheriffs that every day do their job."